One of conventionally known notification devices of an approaching vehicle (which may be referred to as a “conventional device” hereinafter) detects the other vehicle running a crossroad and approaching an own vehicle by a radar sensor.
Specifically, a conventional device transmits a radio wave which has a frequency applicable to a millimeter-wave band (which may be referred to as a “millimeter wave” hereinafter) by a radar sensor, and receives a reflected wave reflected by the other vehicle existing within a transmission range by the radar sensor. The radar sensor generates a signal which has a beat frequency obtained by signal processing of the transmitted wave and the received wave (which may be referred to as a “beat signal” hereinafter) and computes a distance between the radar sensor and the other vehicle in the direction while determining a direction, in which an output peek of the beat signal was detected, as a direction in which the other vehicle exists.
The conventional device acquires (determines) a location (relative position) of the other vehicle with respect to the own vehicle based on the “direction and distance” of the other vehicle thus acquired. The conventional device acquires the relative position of the other vehicle with a predetermined sampling period, and determines the direction of movement of the other vehicle based on the time shift of the position. And, when the conventional device judges that the other vehicle is approaching the own vehicle based on the direction of movement of the other vehicle, it notifies a driver of the own vehicle of that effect along with the direction in which the other vehicle exists. Thereby, the driver of the own vehicle can recognize the fact that the other vehicle is approaching the own vehicle and the direction in which the other vehicle is approaching the own vehicle (which may be referred to as an “arrival direction” hereinafter) (for example, refer to the Patent Document 1).